There is known a breather device which is a ventilation device for air communication between an inside space within a casing of a transmission of a power transmitting system of a vehicle, and an outside atmosphere outside the casing, to prevent an excessive rise of an air pressure in the inside space. JP2016-28926A discloses an example of such a breather device. The power transmitting system disclosed in this publication includes an electric motor accommodated in a motor accommodating casing, as well as a transmission accommodated in a transmission accommodating casing. These motor accommodating casing and transmission accommodating casing are provided with respective breather devices to prevent excessive rises of air pressures within the motor and transmission accommodating casings.
Where the motor and transmission accommodating casings are provided with the respective breather devices independent of each other, as disclosed in JP2016-28962A, two air breather conduits in the form of breather pipes must be installed in communication with air breather outlets of the respective breather devices, while the electric motor and the transmission accommodated in the respective casing are mounted in position in an engine room of the vehicle, such that the air breather conduits do not interfere with other neighboring components. Accordingly, the power transmitting system has a low degree of freedom of arrangement of an air passage system of the breather devices, and suffers from a low degree of ease of mounting of the motor and transmission accommodating casings.